time_t now_real(void);
time_t now_mono(void);
-time_t mono_to_real(const time_t t);
-time_t real_to_mono(const time_t t);
+/* Monotonic times can be negative (a time from before the machine booted) so
+ * treat them as signed. */
+time_t mono_to_real(const int64_t t);
+int64_t real_to_mono(const time_t t);
/* Emits warnings if a call is too slow. */
struct timespec;